- 著者
- Akira TAKASU Yasumitsu SUZUKI Yoshiya OHKI Takahiko OGAWARA Shizue SETO (SAKAMOTO)
- 出版者
- The Association for the Geological Collaboration in Japan
- 雑誌
- 地球科学 (ISSN:03666611)
- 巻号頁・発行日
- vol.76, no.1, pp.37-42, 2022-01-25 (Released:2022-06-25)
- 参考文献数
- 26
Kosmochlor-bearing eckermannite rock is identified in the Yamanobo outcrop of Itoigawa City, Niigata Prefecture, Japan, which is emplaced within a serpentinite body of the Renge metamorphic belt. The eckermannite rock is likely a large enclave within the serpentinite body, with an albitite zone developed between the eckermannite rock and serpentinite matrix. Kosmochlor is lens-shaped or schlieren-like domains within the eckermannite matrix, and comprises spherical aggregates of radiated kosmochloric pyroxene. Spherule cores are occasionally occupied by a corroded form of chromite. The chemical compositions of the kosmochlor exhibit a solid solution between kosmochlor (Ko98Jd0Ae1Q1) and jadeite (Ko25Jd61Ae6Q8). The maximum kosmochlor component is 98 mol.%, likely representing the closest known composition to the NaCrSi2O6 end-member, worldwide. Sodium amphiboles coexisting with kosmochloric pyroxene, and especially the cores of relatively large amphibole grains, in particular, contain high Cr2O3 (up to 12.2 wt.%, 1.34 apfu) and exhibit significant C-site deficiency (i.e., C-site cation < 5).